A bremsstrahlung-photon difference method measurement of the ${\mathrm{Be}}^{9}(\ensuremath{\gamma}, n)$ cross section indicates maxima in the cross section of 1.15\ifmmode\pm\else\textpm\fi{}0.15, 0.55\ifmmode\pm\else\textpm\fi{}0.1, 1.2\ifmmode\pm\else\textpm\fi{}0.2, and 1.0\ifmmode\pm\else\textpm\fi{}0.3 mb at energies of 1.70, 2.40, 2.95, and 4.6 Mev, respectively. The angular distribution of the neutrons corresponding to the 1.70- and 4.6-Mev peaks is spherically symmetric; $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}=a+b{sin}^{2}\ensuremath{\theta}(\frac{a}{b}=1.0\ifmmode\pm\else\textpm\fi{}0.2)$ for the 2.95-Mev peak.

As part of the program to investigate the properties of the Thomas cyclotron, a 20-in. diam proton cyclotron was constructed. In such a three-dee three-phase system it is possible to accelerate protons, deuterons, and tritons at the same setting of frequency and magnetic field but on different modes of the rf. For stable operation in the proper mode and with balanced voltages, it has been found necessary to provide both phase servos and amplifier efficiency servos. The dees could not be servoed individually until the inter-dee capacity was neutralized. Under such conditions it was possible to attain steadily 6.0 ma of protons at 1.0 Mev in the forward mode and 6.5 ma of deuterons at 0.5 Mev in the reverse mode.